The invention relates to a device for heating a liquid in a holder, comprising:
a) a heater element designed for placement in said holder and for immersion in said liquid,
b) a temperature sensor for measuring the temperature of liquid in the holder and coupled to a control unit for the thermostatic control of power supply to the heater element,
c) a thermal cut-out arranged for interrupting the power supply to the heater element in response to heating of the heater element to above a given temperature, which cut-out is in thermally conductive contact with the heater element, and
d) a carrier which is thermally coupled via a thermal coupling to a portion of said heater element, which element is immersed in liquid in said holder in the operational state.
Such a device is known from German utility model DE-U-6944402. Such heating devices are used, for example, for heating fat in deep-frying pans, but they may alternatively be used for heating other liquids, such as water in a water kettle. The current supply to the heater element is thermostatically controlled in dependence on the sensed temperature of the fat, the temperature sensor of the thermostatic control being present in the fat separated from the heater element. If there is an insufficient quantity of fat in the holder, or if the thermostatic control is defective, it could happen that the current supply to the heater element is not switched off and the heater element or the fat present becomes too hot. The latter may even lead to ignition of the fat.
As a safeguard against such undesirable effects, according to the cited German utility model, a heat protection switch is accommodated in a housing which is in contact with the heater element. This heat protection switch forms a thermal safeguard which prevents overheating of the heater element in the situation described above. The housing in this case extends through the bottom of the holder for containing the fat and forms a support for the heater element adjacent a free end thereof.
A disadvantage of this is that the deep-frying vessel, and in particular the heating device thereof, is of a comparatively complicated construction and is accordingly comparatively vulnerable and expensive.
It is an object of the invention to provide a heater element for heating liquid in a holder which is of a simpler construction, while retaining a thermostatic temperature control and a thermal protection of the heater element.
A device according to the invention is for this purpose characterized in that the temperature sensor of the thermostat is situated at a distance from said thermal coupling on said carrier.
Since the temperature sensor and the thermal cut-out are provided in a common housing, a single housing suffices for the accommodation of the temperature sensor and the thermal cut-out. Since the temperature sensor of the thermostatic control is located at a distance from the thermal coupling of the housing to the heater element, said sensor will still assume primarily the temperature of the liquid in the holder during operation. The temperature of the temperature sensor is thus influenced by the temperature of the heater element to a minor degree only. This latter temperature indeed stays within a comparatively narrow temperature range during normal operation.
In particularly advantageous embodiments of the invention:
a) the carrier is formed by a housing which is impermeable to liquids in the operational state when immersed at least partly in liquid, and wherein the temperature sensor and the thermal cut-out are arranged inside the housing (50); and/or
b) the housing (50) is tubular, and the temperature sensor (65) and the thermal cut-out (60) are situated at a distance from one another in longitudinal direction of the tubular housing; and/or
c) the housing and the heater element (31) are constructed as an immersion heater with a portion which is substantially vertical in the operational state and which is designed for extending from an edge region of the housing down into the liquid; and/or
d) the conductors of circuits of which the temperature sensor (65) and the thermal cut-out (60) form part are passed through the housing (50) to the control unit (41); and/or
e) the heater element (31) has a portion (34) which extends mainly in horizontal direction and a portion (33) which extends mainly in vertical direction, the housing (50) extending substantially alongside said vertical portion (33); and or
f) the temperature sensor (65) is situated in an end of the carrier (50); and/or
g) the thermal coupling between the carrier (50) and the heater element (31) is situated adjacent the thermal cut-out (60); and/or
h) the temperature sensor (65) is constructed as an electronic temperature sensor.
The invention may be advantageously used in a deep-frying apparatus whose holder and heating device are designed so as to match to one another.